This invention relates to an impressed current cathodic protection system and more particularly to an impressed current cathodic protection system for a vehicle.
In the prior art impressed current cathodic protection has been used for corrosion protection of metallic members such as vessels, oil rigs, and pipelines. In these applications the cathodic protection consists of bringing the electrolyte potential of the metallic member to an appropriate potential relative to a reference electrode by means of a direct voltage source. For example, for steel, cathodic protection is maintained below -0.80 volt vs. the saturated calomel electrode. The anode, typically of a chemically inert material, is mounted near the metallic member which serves as the cathode.
It has also been suggested that impressed current cathodic protection can be used for the protection of the metallic parts of vehicles such as automobiles, trucks, etc. However, there are some problems in using cathodic protection for a vehicle. First, the electrolyte (typically water due to condensation or road splash) for the cathodic protection is not always present or is not present uniformly in all metallic parts. Second, the power requirements for protecting the metallic parts can be large which would require a large power supply which is undesirable for use in a vehicle. Finally, a large surface area need be protected by the anode.
Accordingly, it is an object of the present invention to provide for an improved cathodic protection system.
It is another object of the present invention to provide a cathodic protection system with a reduced power requirement while still providing cathodic protection to a large surface area.
It is still another object of the present invention to provide a cathodic protection system which is easy and inexpensive in construction and reliable in operation. Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.
Briefly the impressed current cathodic protection system of this invention comprises metallic parts of a vehicle to be protected, a suitable coating, a power source and at least one anode. The coating such as paint, rubber linings, films of synthetic material or the like is applied to the metallic parts to form a protective, electrically insulative coating against corrosion. The coating is also preferably hydrophilic with a high-spreading tendency. An electrochemically active, inert anode preferably with a platinum surface is positioned adjacent to the metallic part while still being electrically separated so shorting does not occur between them when connected to an electrical source of power. The positioning also is preferably at an area of the metallic part where moisture that comes in contact with the part such as condensation, road splash, etc. will be present the longest time thereby maintaining electrolyte continuity between anode and cathode. The negative pole of the power source is connected to the metallic part and the positive pole to the anode so that the electrochemical potential of the metallic part can be kept below a suitable value. Additionally, an electrical current limiting or electrical potential limiting device may be used between the power source and the anode.
In operation moisture acts as the electrolyte in the system between the metallic part cathode and the anode. The anode is mounted in closely spaced, electrically insulated relation to the metallic parts of the vehicle in a location to be electrolytically coupled to any metallic parts of the vehicle exposed through the coating by the electrolyte resulting from wetting of the coating. The use of the corrosion protection coating provides advantages over a bare metal cathodic protection system. The system with the coating has a minimal power requirement and can provide protection for areas far removed from the anode. That is, only the areas of the metallic part that develops defects (scratches and other imperfections in the coating) need current for protection. That means a power supply such as a standard 12 volt battery can be used for supplying the power to the metallic part for extended periods of time. Also as the coating develops more defects with time the cathodic protection system protects corrosion in these areas from taking place.